In this video I derive addition and subtraction identities, cos(x+y) and cos(x-y), using the Law of Cosines and the Pythagorean Theorem. This identity is very useful in all of mathematics and is used in the derivations of many trigonometric derivatives and integrals.
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Related Videos:
Trigonometry Identities: sin(-x) = - sin(x) and cos(-x) = cos(x): http://youtu.be/tD5EA2SXyFQ
Trigonometry: Proof of Law of Cosines (and Pythagorean Theorem): http://youtu.be/wOCYb3Ku6yw
Trigonometry: Sine, Cosine and Tan Functions: http://youtu.be/WKTIlF2oWw8
Trigonometry Identities: cos and sin of angles (2p + x) and (p/2 -x): http://youtu.be/EynSefQs308
Trigonometry Identities: sin(x +/- y) = sin(x)cos(y) +/- cos(x)sin(y): http://youtu.be/edtk9thfwbM .
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I don't always prove the cosine addition and subtraction identities but when I do I usually use both the law of cosines and the Pythagorean theorem in the proof ;)
View video notes on the Hive blockchain: https://peakd.com/hive-128780/@mes/trigonometry-identities-cosine-addition-subtraction
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